[40-Hz auditory steady state response (40-Hz SSR) in patients with intracranial lesions--with reference to consciousness level and sites of lesions].
OBJECTIVE
The issue of whether the 40-Hz SSR could become a useful neurophysiological monitoring tool in the patients with intracranial lesions was investigated.


METHODS
40-Hz SSR was recorded in 50 normal persons and 63 patients with intracranial lesions, and correlation among differences in consciousness level, lesion site and 40-Hz SSR was determined.


RESULTS
(1) Consciousness level and lesion site were both statistically significantly correlated with the pattern of wave forms at a single variable (alpha < 0.0001). (2) Using the multivariate's analysis, an equation to predict the level of consciousness from the SSR waveform and the site of lesion was made. The coefficient of determination between the calculated value and the actual value was 0.822. (3) In the group with intracranial lesions, the P1-N1 amplitude was confirmed to have significantly decreased (alpha < 0.0001) despite a apparently alert level.


CONCLUSIONS
This study revealed that the pattern of 40-Hz SSR waveforms varies with changes in consciousness and lesion site. Moreover, the amplitude of individual waves of SSR waveform is distinctly reduced prior to change the waveform pattern in the alert group. These findings mean that subtle changes of intracranial status could be detected by the continuous monitoring of 40-Hz SSR even at earlier stage of second insult. Consequently, the 40-Hz SSR is a probable objective means of monitoring the consciousness level.
Tachisawa
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Department of Neurosurgery, Tokyo Rohsai Hospital, Japan.
D000328:Adult; D001927:Brain Diseases / Q000503:physiopathology* / Q000523:psychology; D001932:Brain Neoplasms / Q000503:physiopathology; D002561:Cerebrovascular Disorders / Q000503:physiopathology; D003243:Consciousness; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic